As mobile devices become more popular, the demand for longer battery life and instant accessibility increases. With the complexity of a full operating system such as a Microsoft Windows®-based operating system, it is a significant challenge to meet that demand. For example, a typical mobile personal computer boots from an off state (e.g., corresponding to an S5 state according to the ACPI standard) in about twenty to forty seconds, which is clearly not considered to be an instantly accessible device.
Various mechanisms have been attempted to get a computer system back into operation more quickly. For example, an ACPI S3/Standby sleep state has been defined, in which system state is essentially suspended in the system memory, whereby reasonable instant-on performance is achieved. However, the S3 state consumes battery power, which is a concern to many users and device manufacturers, and for at least that reason makes using the S3 state a poor solution for many users. There is also a concern among some users and manufacturers that the S3 state may degrade over time, which is likely due to the various drivers and services, which are obtained from various development sources and that may be part of the critical resume code path.
An S4/Hibernate sleep state is also defined, which in general transfers system memory to a hard disk file to allow a system to wake somewhat more quickly, while also preserving data in the case of a power outage. The S4 sleeping state has the advantage of not consuming any power, but it shares the same stability and potential data loss concerns voiced for the S3 state. Further, an S4 resume still takes approximately fifteen seconds on the average, which also falls short of being considered “Instant-On” solution.
Even with desktop computer systems that are not battery powered, a quick power-on experience is becoming a much sought-after requirement. For example, as many computer systems are evolving towards providing entertainment, particularly home computer systems, there is an increased need to have computing devices act more like consumer electronics devices in order to sell computing products in the competitive computer and consumer electronics marketplace. For example, unlike the aforementioned time of twenty-to-forth seconds for a cold boot sequence, typical consumer electronic devices can be turned on and become functional within a few seconds.
In general, a faster boot from a fully off state is desirable for computer systems. Such a faster boot should be independent of and complimentary to other (e.g., S3 and S4) types of resume operations, because those sleep states preserve system states that are important in some user scenarios.